This invention relates to a voice synthesizing system utilizing a group of representative sound data commonly, and more particularly to a ROM circuit adapted to be used in such a system for reducing required sound data substantially, and also to a method for utilizing the ROM circuit.
In the case where voice signals are synthesized, it has been a known technique to interchangeable use data related to the voiceless sound portions of the signals.
More specifically, the sound portions (p) and (t) in words "PUT" and "PAT" may be interchanged with each other as shown in FIG. 1 without causing any recognizable deviation from the original sound. Any slight deviation caused by such an exchange has imposed substantially no problem so far as the meanings of the words can be discriminated correctly.
At present we are classifying the voiceless sounds into 256 classes or less with representative sound data assigned to these classes.
FIGS. 2(A) and 2(B) illustrate data format (hereinafter termed ROM format) to be used for synthesizing the voice signals. In the drawing, FIG. 2 (A) shows basic blocks KB.sub.1 and KB.sub.2 for the words "PUT" and "PAT", while FIG. 2(B) shows data portions Dp and Dt related to the voiceless sounds in these words. Each of the basic blocks KB.sub.1 and KB.sub.2 comprises a voiceless sound portion M.sub.1, voiced sound portion U, soundless portion K and another voiceless sound portion M.sub.2. On the other hand, the data portion D.sub.p in FIG. 2(B) contains representative voiceless sound data for (p), while the data portion D.sub.t in FIG. 2(B) contains representative voiceless sound data for (t). In the voiceless sound portions M.sub.1 and M.sub.2 in both of the basic blocks KB.sub.1 and KB.sub.2, start addresses SA.sub.p and SA.sub.t (of three bytes) for the representative voiceless sound data are memorized.
Ordinarily the capacity of the address portions memorizing the start addresses increases in accordance with an increase in addressing range as shown in Table 1.
TABLE 1 ______________________________________ Capacity of address por- tions Addressing range ______________________________________ 1 byte upto 256 bytes 2 bytes upto 65536(64K) bytes 3 bytes upto 16777216(16M) bytes 4 bytes more than 16777216(16M) bytes ______________________________________
FIGS. 2(A) and 2(B) illustrate a case where the addressing range is less than 16M bytes. In the above described conventional system, since the voiceless sound portions M.sub.1 and M.sub.2 in the basic blocks directly designate the addresses of the voiceless sound data, the capacity of the address portions has inevitably increased in accordance with an increase in the voice data capacity.